Oh geez, my BF now DH's parents didn't like me when they were just guessing their precious son had a GF, they hadn't even met me yet! I just shrugged it off, it took my husband 4 months to get the courage to introduce me, and they still didn't care too much for me, and I'll admit it's been rocky from that point on.
We ended up getting married at the court house because they were so upset at our decision to get married (after having been together 1.5 years). I think our marriage made them soften up a bit, they have realized I'm not going anywhere...
Are you planning on marrying soon? In my opinion the only opinions that matter are yours and your BF, if his parents don't like you it shouldn't matter unless your BF is overly concerned with having their approval, and if he is then you need to have a talk with him.
Good luck, I'm sure it will pass, they'll get to know you and love you!